The invention relates to improvement in a method of analyzing a reaction rate in chemical analysis used, for example, in the field of medical checks.
In modern medical diagnosis, the checks of tumors for example typically urine and blood is one of indispensable factors. In these checks, the sample to be checked and reagents are distributed into a reaction cell that is moved in a reaction tank whose temperature is kept constant, then after the reaction, the resulting liquid to be measured is illuminated by a photometric light, the absorbance is detected, and thus, for example, the active amount of an enzyme in a serum is measured. In this case, in the analytical method using a conventional reaction rate measuring process, a sample and all reagents required for measurement are mixed, and after a prescribed period of the reaction has passed, the absorbance of the reaction liquid is detected. This "prescribed period" is generally called "lag time" and this lag time has the following three meanings:
(1) The time period which goes from the time when reagents are added to the time when the change in temperature caused thereby stops.
For example, when an enzyme reaction is measured, it is required to keep the temperature constant, and therefore the value of the temperature in the reaction cell during the reaction is to be kept constant at all times. However, in the case wherein the temperature of a reagent that is added in the final stage is different from that constant temperature, since the temperature in the cell changes naturally at the time of the addition, generally the measurement is carried out taking the period required for settling of that change in temperature into consideration.
(2) The time period required for the stabilization of a reaction liquid after the stirring.
For example, after the final reagent is added, the sample and the reagent ar stirred well. At that time, a state unfavorable for the measurement of absorbance, for example, a state wherein bubbles suspend in the reaction liquid continues for a while. Consequently, for accurate measurement the system must wait until the unstable state of the reaction liquid due to the stirring, for example, the presence of bubbles in the reaction liquid disappears.
(3) Lag time of the reaction.
For example the analysis of glutamic oxaloacetic transaminase (GOT) in serum can be expressed by the following two step separate reactions (i.e. equations): ##STR1## In the measurement of enzyme reactions by using NADH, if the reactions include the dehydrogenation reaction of the coenzyme NADH indirectly or directly, the measurement is carried out at around 340 nm. Here, the first reaction cannot be detected optically, but the produced oxaloacetic acid can be related to the second reaction thereby enabling an optical measurement.
In this case, the reduction type coenzyme (NADH) has absorption in the ultraviolet range, the change in absorbance that takes place when the NADH changes to NAD.sup.+ according to the equation (2) is utilized for the measurement of the enzyme active amount of the above GOT, and in order to measure that reaction, the second reaction must be waited until the first reaction proceeds. That is, the reaction according to the second reaction equation (2) is required to be waited until oxaloacetic acid is produced enough to reach the maximum rate in the conversion of NADH to NAD.sup.+ during the reaction of the equation (1). Generally, the lag time including this waiting time until said maximum rate is obtained is called lag time of the reaction. Accordingly, so long as the accuracy of measurement is to be as great as possible, it is required to secure a lag time that will be long enough to expect normal proceeding of reactions with respect to all factors.
Therefore, in conventional methods of measuring reaction rates, the above-mentioned lag time after the addition of all the reagents required for measurement was preset at a longest period in which reactions will proceed as prescribed, and the measured value of the absorbance during that period was excluded in the essential calculation of the measurement of the absorbance.